What makes an under-stressed engine?
Discussion
Its all about having enough metal in the right areas and in the right configuration.
If someone tells you that theyre going to DOUBLE the output of their engine by forced induction, you'd probably be thinking that the forces acting on the internals are also going to double.
Thankfully thats not true.
By doubling the output of an engine, the peak pressures in the cylinder reach roughly 20% higher, so its not really as bad as it looks at first sight.
Head gaskets have to be up to the job, but even standard ones can take a lot of abuse before letting go.
The absolute killer of engines, is usually revs.
Higher revs induces massive loadings on conrods, out of all proportion to the extra revs used, this is why rod bolts can let go in a big way, the forces acting on them are so huge.
Special materials and designs are necessary to prevent such catastrophic failures.
There are basically two loads relevant to an engine structure whilst its in operation; inertia loadings and power loads.
Inertia loads can be either compressive or tensile(pulling apart), power loads are only compressive.
If an engines speed is increased by X3, the inertial loads shoot up by around X9!!!
A large displacement engine running at 7000rpm can develop con rod inertial loads greater than 4000psi!
If someone tells you that theyre going to DOUBLE the output of their engine by forced induction, you'd probably be thinking that the forces acting on the internals are also going to double.
Thankfully thats not true.
By doubling the output of an engine, the peak pressures in the cylinder reach roughly 20% higher, so its not really as bad as it looks at first sight.
Head gaskets have to be up to the job, but even standard ones can take a lot of abuse before letting go.
The absolute killer of engines, is usually revs.
Higher revs induces massive loadings on conrods, out of all proportion to the extra revs used, this is why rod bolts can let go in a big way, the forces acting on them are so huge.
Special materials and designs are necessary to prevent such catastrophic failures.
There are basically two loads relevant to an engine structure whilst its in operation; inertia loadings and power loads.
Inertia loads can be either compressive or tensile(pulling apart), power loads are only compressive.
If an engines speed is increased by X3, the inertial loads shoot up by around X9!!!
A large displacement engine running at 7000rpm can develop con rod inertial loads greater than 4000psi!
as deltaf says, rpm is the killer and to make an engine rev more costs big bucks. The old buick is a low revver delivering bucketfulls of torque.....which is nice 
deltaf said: Its all about having enough metal in the right areas and in the right configuration.
If someone tells you that theyre going to DOUBLE the output of their engine by forced induction, you'd probably be thinking that the forces acting on the internals are also going to double.
Thankfully thats not true.
By doubling the output of an engine, the peak pressures in the cylinder reach roughly 20% higher, so its not really as bad as it looks at first sight.
Head gaskets have to be up to the job, but even standard ones can take a lot of abuse before letting go.
The absolute killer of engines, is usually revs.
Higher revs induces massive loadings on conrods, out of all proportion to the extra revs used, this is why rod bolts can let go in a big way, the forces acting on them are so huge.
Special materials and designs are necessary to prevent such catastrophic failures.
There are basically two loads relevant to an engine structure whilst its in operation; inertia loadings and power loads.
Inertia loads can be either compressive or tensile(pulling apart), power loads are only compressive.
If an engines speed is increased by X3, the inertial loads shoot up by around X9!!!
A large displacement engine running at 7000rpm can develop con rod inertial loads greater than 4000psi!
Clearly a man of my own heart. Who needs a stroked/sleeved RV8 and the costs/risks that go with it when a turbo or 2 will do the job even on stock 9:1 c/r appx so long as you use stock rpm. You can use the turbo's with a Holley if you like. Oh, 5.0 Rovers are stressed if the valve gear is uprated. They all show excessive valve train wear.
Yeah James thats true. Oversquare and usually short stroke, makes for a high revver, average piston speeds are lower than with an equivalent long stroker of the same displacement.
I used to have an Audi fitted with the 5 cylinder engine. I did a lot of work with regard to figuring out all about these engines, ie; dimensions, differences with rods, gudgeon pins etc etc.
I had a plan to build a short stroke 2.1 (5 cylinder) that would rev reliably to 9000rpm, the reason being that i was going to use the shorter 1.9litre crank, it had a throw of 77.4mm as opposes to the 2.3 i was using at some 86.4 mm stroke.
Unfortunately my plans got wasted by someone writing off the car...lol (no not me)
I used to have an Audi fitted with the 5 cylinder engine. I did a lot of work with regard to figuring out all about these engines, ie; dimensions, differences with rods, gudgeon pins etc etc.
I had a plan to build a short stroke 2.1 (5 cylinder) that would rev reliably to 9000rpm, the reason being that i was going to use the shorter 1.9litre crank, it had a throw of 77.4mm as opposes to the 2.3 i was using at some 86.4 mm stroke.
Unfortunately my plans got wasted by someone writing off the car...lol (no not me)
eliotmansfield said: And remind we why you would want to rev it to 9000rpm?
I know that F1 engines rev so high is becuase they are limited by displacement, therefore they spin it higher to get more air thru it. But why would you want to do it on a production engine?
Why not, if you are able to. More revs = more power = more fun.
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